The invention relates to a method of searching, in an assembly of non-uniformly distributed points, the point which is the nearest from of a characteristic of a given analog signal. The invention also relates to a receiver comprising means for receiving an analog signal, and decoding means for selecting, in an assembly of non-uniformly distributed points, the point which is the nearest from a characteristic of the received signal. The invention further relates to a transmission system comprising such a receiver.
The invention finds important applications, notably in modems of the PCM (Pulse Code Modulation) type, and particularly in modems conforming to the recommendation V.90 of the ITU (International Telecommunication Union).
U.S. Pat. No. 4,143,363 describes a method of determining the quantization level associated with an analog signal by applying a segmented linear logarithmic compression law. This method comprises the step of determining, from an assembly of non-uniformly distributed levels, the level which is the nearest from the amplitude of the received analog signal. The proposed method takes certain properties of the compression law into account: particularly it takes account of the fact that the linear segments each comprise the same number of points.
This is a specific method which is connected with the law of distributing points in the assembly considered. Particularly, it is not applicable to the detection of symbols received by a VPCM modem because the constellations used by the PCM modems only comprise certain points of a law for segmented linear logarithmic compression.
The invention notably has for its object to provide an efficient method of determining, in an arbitrary assembly of non-uniformly distributed points, the point which is the nearest from a characteristic of a given analog signal.
This object is achieved by means of a method as defined in claim 1 of this application. The proposed solution consists of effectuating a dichotomy on the number of points comprised in the search interval. It is independent of the law of distributing points in the considered search assembly.